The sprawling Bagram base, or the equally large Kandahar Air Field, are attractively large targets for militants who might not have the stomach to launch a frontal assault on foreign or Afghan troops.

NATO officials today said they were unsure of the exact type of weapon fired at Bagram, which immobilized General Dempsey’s C-17 transport plane and slightly injured two American maintenance crew, but Chinese-made 107mm rockets are one of the most common used in such attacks.

The rockets can be easily set up on a rock or another firm surface and crudely aimed in the direction of its target, sometimes up to three miles away. Accuracy is mostly guesswork, which probably explains why there are comparatively few casualties despite them being a common occurrence.